The present invention relates generally to thermal protectors, and more particularly to a thermal protector for use with a wattage lamp mounted in a recessed lighting fixture.
Recessed lighting fixtures are commonly installed in residential and commercial environments, particularly in installations in which the architect or designer wishes the light source to be relatively unnoticeable. Conventional ceiling recessed lighting installations are described, for example, in U.S. Pat. Nos. 5,222,800; 5,457,617; 5,452,816; 5,347,812; and 4,646,212. In a recessed lighting installation, the light source is contained in a housing which is mounted in a space in the ceiling. The lamp housing is, in turn, mounted to a frame which is secured to the structural supports of the ceiling, such as to the wood joists that support the ceiling.
Depending upon the applicable building codes that deal with electrical and thermal considerations, as well as the goals of the lighting designer, the ceiling space or environment in which the lighting fixture is installed may be either insulated or non-insulated. Fixtures installed in the ceiling space must, as a result, be rated for use in insulated or non-insulated ceilings as appropriate. A ceiling environment that is insulated will tend to retain heat generated by the light source in the lighting fixture more than one that is not insulated.
A ceiling which is not initially insulated during building construction may be retrofitted with thermal insulation at a later date. Recessed lighting fixtures that were originally installed may become overheated after insulation is added because the fixtures may not be rated for use in insulated ceilings.
The use of an improper type or wattage of the light source (bulb) in a recessed lighting fixture or in an incorrectly rated fixture can create hazards, such as the creation of a temperature in the surrounding region that is higher than the fixture (and possibly the surrounding insulation) is able to accommodate. Improper bulb conditions or the use of inappropriately rated recessed lighting fixtures can thus create a potentially dangerous condition with respect to thermal conditions that could constitute a fire hazard.
In recognition of this potential for overheating and its concomitant potential hazards, the National Electrical Code and Underwriters Laboratories Inc. product standards require that recessed lighting fixtures be provided with thermal protectors in order to reduce the risks associated with the improper installation or use of the light source or fixture. When the temperature sensed by the thermal protector exceeds a predetermined maximum level, indicating an overheating condition and a possible fire hazard, a switch, typically a bimetallic switch associated with the thermal protector, opens to disconnect the lamp from the power line, and the lamp is turned off. When the temperature in the space around the thermal protector then falls below the preset dangerous level, the switch closes and the lamp is reconnected to the power line and turns on.
This opening and closing of the thermal protection switch causes the lamp to flash on and off, thereby to indicate the existence of a potentially dangerous overheating problem in the lighting fixture, while preventing the temperature in the fixture from being maintained at a potentially dangerous level. Although thermal protection of this type is commonly used in a recessed lighting fixture, similar thermal protection may also be employed in other types of lighting installations, in which overheating could cause a direct fire hazard.
Commercially available thermal protectors, which are intended for use in a recessed lighting fixture, are rated for limited electrical loads, typically 600 watts, that corresponds to the high-end rating of the most commonly used single lamp socket. Such a limitation in the capacity of the thermal protector may, however, present a problem in lighting fixtures and lighting systems that draw higher electrical loads, such as up to 1000 watts or more that exceed the rating of the thermal protector. Switching a 1000-watt load with a bimetallic switch rated at 600 watts could cause the switch to fail. The failure may result in the switch welding to a closed or "on" position, which would cause the lamp to remain energized or "on". Accordingly, high-wattage lighting fixtures, i.e. those operating at loads greater than 600 watts, cannot be readily provided with code-required thermal protection. Increasing the capacity of the thermal protector is not a practical option since that would substantially increase its cost and size.
There is thus a current need for a thermal protector that can be safely and reliably used in lighting fixtures in which the load exceeds the thermal protector's electrical power rating.